Integrated services digital network (ISDN) communications enable telephone service providers to supply multiple types of signalling channels from a central office over a single twisted pair-configured, local loop to a network termination interface or ISDN terminal equipment, such as, but not limited to an ISDN phone, an X.25 packet device, or an ISDN terminal adapter, to which customer premises-resident data terminal equipment may be coupled.
These multiple types of signalling channels typically include a digital data channel, a digitized voice channel and a separate dialing channel. Since the ISDN terminal equipment is customer-installed, the local telephone service provider does not participate in the customer's choice of equipment to be connected to the ISDN line.
However, in order for a customer to actually place a call through an installed piece of terminal equipment, it is necessary that the terminal equipment's supervisory communications controller be properly initialized or preconfigured with a prescribed set of communication parameters. These parameters include the telecommunications switch protocol employed in the local service provider's central office facility, the local directory numbers (LDNs), including area codes, associated with the two ISDN bearer (B1, B2) channels, and a service profile identifier or SPID. The SPID is a sequence of digits, which identifies the ISDN terminal equipment that is coupled to the ISDN switch, and is assigned by the local telephone service provider, when the ISDN line is installed. The number of SPIDs required (0, 1 or 2) will depend upon how the ISDN line is configured.
Now although the switch protocol and SPID parameters are routinely supplied by the telephone service provider to the purchaser of the ISDN terminal equipment equipment, the user is usually technically unsophisticated and accustomed to doing nothing more than simply installing an analog modem in the customer's premises-located equipment, and plugging in a telephone connector to a modem port (RJ 11 jack). Indeed, experience has shown that on the order of eighty percent of ISDN customers will burden the equipment supplier and/or the local telephone service provider with requests for technical support in the course of configuring the settings for ISDN terminal equipment, irrespective of whether the service provider has correctly assigned each of the switch protocol, SPID and LDN parameters for use by the customer's ISDN terminal equipment.